This study aimed to improve students' mathematical reasoning ability on
mathematics learning through Discovery Learning of the Two Stay Two Stray
(TS-TS) strategy. The subjects of this study were all the eighth graders of class G
at SMP Negeri 1 Sumbang which consisted of 34 students. This research was
conducted in 3 cycles, consisting of 2 meetings in each cycle. Each cycle
consisted of action planning, action implementation, observation and reflection.
Data collection techniques conducted by researcher were observation and test of
students' mathematical reasoning ability. Based on the results of the study,
students' mathematical reasoning ability in cycle I obtained an average score of
60.00, in cycle II it raised to 63.94 and in cycle III it reached at 72.97. From the
results of the students' mathematical reasoning ability test in the first cycle to the
third cycle, it could be concluded that learning through Discovery Learning of
the strategy of Two Stay Two Stray (TS-TS) was able to improve students'
mathematical reasoning ability for the eighth graders of class G at SMP Negeri 1
Sumbang especially on three-dimentional geometry.